Key Engineering Materials Vols. 326-328

Abstract: A system was developed for simultaneously measuring stress and temperature in structures in time series. The stress and temperature were measured using the photoelastic technique in the form of phase stepping and the thermographic technique, respectively. Four phase-stepped photoelastic images were captured simultaneously using beam-splitting optics. A beam splitter was used for transmitting light in the visible range while simultaneously reflecting light in the infrared range. The system was applied to ultraviolet curing resin with a step part illuminated with ultraviolet rays, and the stress and temperature in the curing process were measured. Results showed that the stress and temperature in the curing process can be measured simultaneously in time series using the system. The step part of the resin affected the distribution of the stress and temperature

Abstract: In the present study, the flow structure inside the refrigerating compartment of a scaleddown display cooler model was investigated experimentally using the particle image velocimetry (PIV) method, which is a reliable velocity field measurement technique. In addition, we also carried out flow visualization and computer simulations regarding the movements of thermo-fluid inside a display cooler. As a result, the velocity field measurement shows a large scale vortical flow structure inside the refrigerating compartment due to the entrained flow, thus penetrating a base plate through the open inlet gap.

Abstract: In this paper, a novel optical method, namely, Coherent Gradient Sensing (CGS) is used to study the fracture properties of IR window materials in the guidance missile. CGS can produce high contrast fringes and provide some degree of control on the sensitivity of measurement during experiment. It is highly attractive for solid mechanics applications, especially to new materials, such as IR window materials. But the accuracy of the fringe order in the CGS interference image will deeply influence the precision of experiment. Because of the different optical principle from other method, the fringe order of CGS can’t be obtained through the phase-shift technology. To satisfy the precision request of IR window materials, a kind of modified CGS method, loading CGS method is introduced and analyzed, which can accurately obtain the fringe order of random position in the CGS interference image. This method doesn’t need additional optical set-up and complicated image processing techniques, but only need two CGS interference images under different loading. Static fracture experiments of ZnS show that this method can evidently improve the precision of the CGS method.

Abstract: In this study we have experimentally and numerically analyzed the flapping mechanism and wing kinematics of coleoptera (Propylea japonica Thunberg). Using digital high speed camera, we captured the continuous wing kinematics and visualized the flight motion of the free-flying coleoptera. The experimental visualization shows that the elytra flapped concurrently with the main wing both in the downstroke and upstroke motions. In order to define the wing kinematics of coleoptera, the displacement of a wing cross section (50% span-wise) was measured for each sequence of the wing motion. Using these data, the flight motion of coleoptera was numerically simulated to investigate the aerodynamic performance. The computational aerodynamic simulation shows that leading edge vortex shedding plays a key role in generating lift to keep the insect aloft.

Abstract: This study is launched to get exact bore-sighting value in the process of assembly for XK11. Image processing method with Charged Coupled Device camera is chosen for the Error reduction of bore-sighting. The results of this method by using a CCD camera and the Testing Target Method are described in this paper. After we confirm the performance of the Dual-Barrel Weapon and that of the Firing Control System in the Dual Barrel Weapon System, the bore-sighting which is a part of the process in the system assembly is accomplished. In this process, the position of the barrel is identified by using the Testing Target Method that is an existing bore-sighting method. Then the fixing line of the Firing Control System is checked by a Day-Optical part. The precision of the boresighting is required within 1 mil, however the manual method using the human eyes makes it worse. Therefore CCD camera is installed in the eyepieces. Next, we can get the image of the sighting and the center coordinate values of the laser-pointer from each barrel by image processing method. Required bore-sighting value is calculated from the eccentricity of the center coordinate. Finally, we will plan to adopt this result in the assembly process of XK11.

Abstract: Rheo-optical and mechanical properties of Cyclic Olefin Copolymers(COC’s) with different composition have been investigated across the glass transition temperature. Accurate measurement of stress or strain-optical coefficients and elastic modulus data across the glass transition are essential for predicting optical anisotropy in many optical products like pickup lenses and waveguides in LCD backlight unit since the material of these products have both flow and thermal history from the melt to glass. To obtain stress-optic behavior in the wide frequency region including rubbery, glassy and glass transition regime, extensional bar-type device was used. A shear-sandwich tool was used in the melt region. Master curves for modulus, stress-optical and strain-optical coefficients have been obtained in wide frequency region. The stress-optical coefficients of COC’s with mol fraction of norbornene, 60 ~ 70%, showed almost constant between -8 and -9 Br at glassy region and between +920 and +1,160 Br in the melt region. Even though the glass transition temperature showed the difference of 35
, the stress-optical coefficients of COC’s with different composition showed almost same extreme values

Abstract: Recently, injection molded plastic optical products are widely used in many fields, because injection molding process has advantages of low cost and high productivity. However, there remains residual birefringence and residual stresses originated from flow history and differential cooling. The present study focused on developing a technique to measure the birefringence in transparent injection-molded optical plastic parts using two methods as follows: (i) the two colored laser method, (ii) the R-G-B separation method of white light. The main idea of both methods came from the fact that more information can be obtained from the distribution of retardation caused by different wavelengths. The comparison between two methods is demonstrated for the same sample of which retardation is up to 850 nm.

Abstract: This paper presents a new optical configuration for measuring the phase retardation of optical linear birefringent materials. Phase retardation is measured by a heterodyne light source, which is generated by a Zeeman laser. The measurement system has advantages as a simple optical setup, high stability, small size, and portable owing to the configuration and the use of a Zeeman laser. Using the ratio of amplitudes from two measured heterodyne signals, a simple algorithm can obtain the phase retardation directly. Moreover, we can extend dynamic range of the phase retardation measurement to be 0 180 successfully. According to the experimental results, the average absolute error for the phase retardation of λ / 4 -wave plate sample is determined to be only 2.7 %.

Abstract: The formation and growth mechanism of polysilicon grains in thin films via laser annealing of amorphous silicon thin films are studied. The complete understanding of the mechanism is crucial to improve the thin film transistors used as switches in the active matrix liquid crystal displays. To understand the recrystallization mechanism, the temperature history and liquidsolid interface motion during the excimer laser annealing of 50-nm thick amorphous and polysilicon films on fused quartz substrates are intensively investigated via in-situ time-resolved thermal emission measurements, optical reflectance and transmittance measurements at near infrared wavelengths. The front transmissivity and reflectivity are measured to obtain the emissivity at the 1.52 μm wavelength of the probe IRHeNe laser to improve the accuracy of the temperature measurement. The melting point of amorphous silicon is higher than that of crystalline silicon of 1685 K by 100-150 K. This is the first direct measurement of the melting temperature of amorphous silicon thin films. It is found that melting of polysilicon occurs close to the melting point of crystalline silicon. Also the optical properties such as reflectance and transmittance are used to determine the melt duration by the detecting the difference of the optical properties of liquid silicon and solid silicon.